Force disturbance compensation for an AC brushless linear motor

The paper presents two methodologies which are able to compensate for the disturbance forces produced in brushless AC linear motors. This force, while depending on a number of reasons, is mostly due to the cogging resulting from both the motor anisotropic reluctance and the edge effects. A short description of a linear motor drive is given and a model of the assembly is suggested. A series of laboratory tests are then presented in order to define the parameters of the system and to characterise the force disturbance. This force, which affects the motor trajectory path (speed and position), can be counteracted by the algorithms proposed. The first is based on a static feedforward compensation of the noise, implemented by reconstructing and compensating a disturbance with the same harmonic content derived from the measurements. A second technique is based on a closed loop regulator, which implements a state observer, also tuned on the basis of the laboratory tests. The results of simulation and comparison of the algorithms proposed both give encouraging results useful for their actual implementation.